Hubble observations of nearby starburst galaxies challenge the idea that supernova winds helped reionize the early universe, suggesting young stars may have enabled radiation to escape before those winds formed.

Powerful winds from exploding stars were thought to clear paths for ultraviolet radiation to escape early galaxies. A new study of nearby galaxies suggests those winds may instead make escape more difficult, challenging a leading explanation for how the universe emerged from a fog of neutral hydrogen.

Within the first billion years after the Big Bang, that fog made the universe opaque to ultraviolet light. It began to clear during an era called reionization, which started about 13 billion years ago. Energetic radiation from early galaxies struck neutral hydrogen atoms, separating them into charged protons and electrons.